Sudden overheating

[ThomasOFP]

Hello my friends,

i have a big problem with my MY98 BMW 535i V8. Its M62B35S1 non Vanos engine. Year ago i overheated my car on the highway due to waterpump failure. I repaired my car, changed some parts except thermostat (stucked open, so my normal temperature is about 70°C) and head gaskets. Now i have problem with sudden overheating. My car runs fine engine is going little rough but not so much. If i am driving abou 10 miles, my temperature gauge hits red line in one second. If i stop the car and check engine, nothing seems to be bad. I can hold my hand on water hoses, its not really hot and if i open the cap on water tank, water is not boiling. I thought about cracked heads or head gaskets, so i tried test with block checker kit and the liquid stayed blue. Sometimes the temperature gauge get back in the 1/3 of field , sometimes it stay at red field for minutes. Once i hit my destination and pulled car over. when i returnet after 2 hours, temperatuer gauge hit red field even without starting the engine. Inpa says 139 activation map cooling error, which is dead thermostat. Other option is air bubble in cooling system, but i tried bleed my car milion times and nothing helped. Can failed thermostat caudse overheating if stucked open? please help me. Thanks for answers. Tom

[edjack]

Certainly is possible, with engine running at such a low temperature, that the cooling system pressure is allowing hot spots.

Before you do anything else, replace the thermostat. Use this bleed procedure.

Bleed Cooling System BMW method

On your I6, you need to raise the front end of the car up as high as you can to get the air to the front of the engine.

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Cooling system bleed procedure (E39)

- with cold car
- top up coolant to proper level (even slightly higher will not hurt at this stage)
- leave rad cap loose

This stage bleeds air trapped in the heater system.
- turn on ignition switch to position 2 (no start)
- set temperature selectors on the climate control to max temp.
- manually set the fan speed to low (lower end of speed range)
- start engine (check that climate settings have not changed)
- after 5-10 seconds of running rev the engine 3-4 times to about 2500 RPM - hold there for about 5 seconds each time.
- shut off engine (should not run for much longer than about 30 seconds - you just want to shut if off before it starts to generate any heat and expand the coolant).
- inspect the coolant level and top up again if necessary.
- tighten the coolant fil cap.

This stage bleeds air from the engine, rad and fill tank.
- now warm up the engine (drive a bit if you wish)
- with engine running CAREFULLY / SLOWLY open the bleed screw. Hold a rag around the area to prevent any excess splashing. Keep the screwdriver in the slot of the bleed screw so you can close it quickly.
- you should have some air/steam escape - progressing to some bubbles of coolant.
- as soon as it progresses to the stage where you are seeing liquid coolant come out then close the bleed screw. Do not over tighten - it is all plastic threads and you can easily turn too far at which point the screw jumps back a thread and you have to re-tighten. Just make it snug with all coolant stopped.
- when the car is cold again re-check the coolant level and top up again if necessary.

NOTE - some of the 6 cyl models have 2 bleed screws - the second one is near the thermostat. In that case you should bleed at both locations (one at a time)

You may have to repeat the bleed procedure 1 or 2 more times over the next week. Can "probably" skip the stage for the cold start bleeding of the heater system.

If the level continues to fall below the correct level then have the system fully pressure tested - explaining to your service manager what you have already done.

It is very important that all leaks be sealed so that the system can operate at full pressure. The engine computer is programmed to keep the coolant temp at about 108C at "most" times (there are exceptions) and the only way it can maintain that temp is if the pressure can be maintained - system fully sealed.

Cheers
Jim Cash

[ThomasOFP]

I will order a new tstat asap. Thank you for bleeding manual. I have also suspition that coolant temperature sensor may give false readings.

[edjack]

INPA should allow you to monitor coolant temperature. You can also unlock the instrument cluster, and, using test 7, monitor coolant temp.

[ThomasOFP]

I unlocked instrument cluster to check the temperature. It keeps between 67 - 70 degrees and then jump to 128°C in one step